1. Field of the Invention
The present invention relates to an ignition timing control apparatus of an internal combustion engine, more particularly to an ignition timing control apparatus for improving driving characteristics directly after engine startup.
2. Description of the Related Art
In a spark ignition type internal combustion engine, generally in the state where the temperature of the coolant is low or in the state directly after startup where the temperature of the combustion chamber is extremely low, the aeration of the fuel deteriorates and also the combustion speed slows down, resulting in unstable combustion. This results in such disadvantages as unstableness of the idling speed and inferior driving characteristics.
To eliminate such disadvantages, control has conventionally been effected to increase the amount of fuel supplied while the coolant temperature is low or directly after startup, to make the ignition timing more advanced in angle while the coolant temperature is low, etc. However, such methods of control have not been able to achieve fully satisfactory driving characteristics directly after startup when the combustion chamber is coldest. If it is attempted to increase by a massive amount the amount of fuel supplied directly after startup so as to improve the driving characteristics, the ignition plugs are liable to become sooty. Further, if the percent of change of the advance angle correction to the change of the coolant temperature is uniformly increased, knocking is liable to occur. This is because the coolant temperature does not represent the temperature of the combustion chamber of the engine. For example, even when the coolant temperature is 0.degree. C., the combustion chamber temperature differs in the case when starting from -30.degree. C. and rising to 0.degree. C. and the case when starting from 0.degree. C. In other words, in the latter case, the temperature of the combustion chamber is low. Therefore, in the latter case, the ignition timing is too far in advance of the desired value and knocking is liable to occur.